Disorders involving opioid use are a severe problem among jail and prison inmates. Inmates in the US, Canada, Australia, and many European and Asian nations have disproportionately higher rates of opioid use disorders than their general populations. Scarce resources are provided for corrections-based substance use treatment in many nations, and many inmates with OUDs remain untreated. The use of long-acting, injectable naltrexone (XR-NTX) may be a promising form of treatment for pre-release prisoners. Naltrexone blocks the intoxicating and reinforcing effects of opioids, but has no opioid-like effects. This proposed five-year study will focus on whether the addition of providing XR-NTX treatment at a patients' place of residence will increase adherence and thus efficacy of the medication. Project implementation will occur at five pre-release prisons under the jurisdiction of the Maryland Department of Public Safety and Correctional Services (MDPSCS): 1) Metropolitan Transition Center (MTC) for men; 2) Baltimore Pre-Release Unit (BPRU) for men; 3) Jessup Pre- Release Unit (JPRU) for men; 4) Baltimore City Correctional Center (BCCC) and 5) Maryland Correctional Institution (MCI) for Women. Following initial screening, informed consent, and medical examination, pre- release prisoners at each facility will be block randomized (N=240) within gender to either: Condition 1. XR- NTX-OTx (n=120): One injection of XR-NTX in prison, followed by six monthly injections post-release in the community at an opioid treatment program; or Condition 2. XR-NTX+MMTx (n=120): One injection of XR-NTX in prison, followed by six monthly injections post-release in the community at the patient's place of residence. All participants will be confirmed opiate-free by urine test and negative naloxone and oral naltrexone tests, and evaluated monthly for seven months and 12 months after release from prison. The proposed study has two specific aims: Aim1. To compare the two study conditions in terms of: a) XR-NTX treatment adherence; b) opioid use; c) criminal activity; d) re-arrest; e) re-incarceration; and f) HIV risk-behaviors (i. needle use; ii. risky sexual behaviors). Aim 2. To determine if the number of months of post-release XR-NTX treatment is related to outcome (a-f above), and if so, is there a point at which XR-NTX v. Non-XR-NTX equilibrates? This would help determine the number of injections, important because of XR-NTX cost. Many individuals in the criminal justice system drop out of treatment and therefore increasing ways to improve adherence by attempting to: 1) expand capacity; and 2) implement access by providing treatment at their place of residence may positively impact outcomes.